1. Field of the Invention
The present invention relates to a cleaning device, and an image forming apparatus and a process cartridge that include the cleaning device.
2. Description of the Related Art
In general, an image forming apparatus using an electrophotography process includes a photosensitive material as an image carrier. Electric charge is applied through discharge to the surface of the photosensitive material for charging the photosensitive material, and the charged surface of the photosensitive material is exposed to form an electrostatic latent image. This latent image is then supplied with toner to be a visible image. The visible image formed on the surface of the photosensitive material is transferred and fixed onto the surface of transfer paper. The transfer paper with the visible image is delivered outside the image forming apparatus.
The photosensitive material after transfer of the visible image has untransferred toner and other substances left on its surface. Therefore, to prevent these substances from affecting the next image formation, the surface of the photosensitive material after transfer is cleaned by a cleaning device for preparing for the next image formation process. An example of such a cleaning device generally known is the one in which a cleaning blade formed of an elastic body, such as rubber, slidably scrubs the surface of the photosensitive material to remove attachments, such as untransferred toner.
However, with such a configuration of the cleaning blade that removes attachments with a blade in a mechanical manner, the residue tends to be accumulated between the surface of the photosensitive material and the tip of the blade making contact with the surface of the photosensitive material. Therefore, when the next untransferred toner is delivered with a certain amount of residue accumulated therebetween, a cleaning failure tends to occur, in which the untransferred toner goes through as it is without being scraped by the blade.
Also, in recent years, with increasing demands for high image quality and high definition of images, toner made of round particles with a small particle diameter has been used in a developing process. With the use of such toner, the toner can be closely attached to an electrostatic latent image, thereby achieving high image quality and high definition.
However, such toner made of round particles with a small particle diameter tends to go through the cleaning blade in a cleaning process, thereby posing a problem of a cleaning failure. Moreover, since the surface of the photosensitive material wears out, the life of the photosensitive material is shortened.
To get around the problems and solve inconveniences, such as abrasion of a cleaning member and the photosensitive material, a scheme has been taken in which a lubricant is applied onto the surface of the photosensitive material, for example, to reduce a friction resistance between the photosensitive material and the cleaning member. Also, if a lubricant is applied onto the surface of the photosensitive material, a friction resistance on the surface of the photosensitive material can be reduced. Therefore, an effect of preventing the occurrence of so-called filming can be obtained. Filming is a phenomenon in which a superplasticizing agent, a charge-controlling agent, and other agents added to the toner are fixed onto the surface of the photosensitive material due to abutting pressure of the cleaning member, thereby forming a film. Furthermore, since the attachment force of the toner developed on the photosensitive material is also reduced with respect to the photosensitive material, transferability is increased.
Examples of a unit for applying a lubricant onto the surface of the photosensitive material include one with a solid lubricant formed of, for example, fatty acid metallic salt, in a stick-like shape, and a brush roller having brush bristles the tips of which contact both of the solid lubricant and the photosensitive material. With such an applying unit, when the brush roller is rotatingly driven, the solid lubricant is shaved through a sliding scrub by the rotatingly-driven brush roller to become powder. This powder-like solid lubricant is then attached to fibers of brush bristles of the brush roller. Next, the powder-like lubricant attached to the brush roller is applied onto the surface of the photosensitive material positioned downstream of a rotating direction.
To efficiently function this applying brush roller for applying the lubricant onto the surface of the photosensitive material, in some cases, a cleaning brush roller is provided on an upstream side of the applying brush roller, the cleaning brush roller for scraping untransferred toner and other substances off the surface of the photosensitive material. Since untransferred toner is attached to the surface (brush bristles) of the cleaning brush roller, a flicker is fixedly arranged to contact the cleaning brush roller. With this flicker, the attached toner on the cleaning brush roller is scraped off to a waste toner path.
In this manner, in recent years, one scheme has been adopted as a scheme of cleaning the photosensitive material in which two brush rollers, one for additional cleaning and the other for applying a lubricant are provided to increase cleaning ability.
An example of an image forming apparatus adopting the scheme described above is the one including: a cleaning aid unit that partially removes attachments on a latent-image carrier; a lubricant applying unit provided at a downstream side of the cleaning aid unit in a direction of delivering a transfer material, the lubricant applying unit applying a lubricant on the surface of the latent-image carrier; and a cleaning blade provided at a downstream side of the lubricant applying unit in the direction of delivering the transfer material, the cleaning blade scraping residual toner off the latent-image carrier (for example, refer to Japanese Patent Application Laid-Open No. 2004-325823 (pp. 1-2, FIG. 1)). Therefore, according to this image forming apparatus, transfer unevenness due to a cleaning failure can be prevented, thereby achieving high image quality. That is, with the cleaning aid unit, part of the attachments are first removed from the latent-image carrier, and then, with the lubricant applying unit, the lubricant is applied onto the surface of the latent-image carrier. Therefore, the lubricant can be applied evenly. For this reason, friction between the surface and the tip of the blade can be kept constant. As a result, the residual attachments can be reliably scraped by the cleaning blade, thereby preventing the attachments from being accumulated.
Also, a cleaning device has been known that is configured to include: a bristle brush roll having a perimeter surface provided with a bristle brush portion with a loop-pile-shaped filling structure, the bristle brush portion formed with a spiral groove portion; and a cleaning blade abutting on an image carrier, such as a photosensitive drum, wherein the bristle brush roll scrapes a developing agent remaining on the photosensitive drum through rotation of the bristle brush roll, the scraped developing agent is delivered along the groove portion in an axial direction, and the cleaning blade scrapes and removes the residual developing agent that was unable to be removed by the bristle brush roll (for example, refer to Japanese Patent Application Laid-Open No. H8-160819 (pp. 2-4, FIGS. 1 and 2)). Therefore, according to the cleaning device, with the loop-pile-shaped filling structure of the bristle brush portion, loss of bristles can be prevented. Also, a situation can be prevented such that a lost bristle is inserted between the cleaning blade and the image carrier, thereby preventing the image carrier to be damaged and also preventing the occurrence of a cleaning failure. Still further, with the spiral groove on the bristle brush portion, the scraped developing agent can be delivered. Therefore, unlike the conventional technology, no mechanism for delivering the developing agent is required, thereby achieving a reduction in configuration.
Furthermore, an image forming apparatus using an image forming method has been known in which, after the image carrier is charged and image-exposed to light to form an electrostatic latent image, the image is made visible by a developing agent, and then undergoes transfer and cleaning processes for image formation, the image forming apparatus including a lubricant applying device that evenly applies a lubricant made of lubricating oil or lubricating grease onto the image carrier to form a thin film, with the use of a brush-shaped rotating body arranged to contact the image carrier, and an application amount controlling device that controls the amount of application of the lubricant (for example, refer to Japanese Patent Application Laid-Open No. H11-212398 (pp. 2-4, FIGS. 3 to 5)). Therefore, according to this image forming apparatus, the amount of reduction in film thickness of a photosensitive layer can be suppressed as much as possible, squeak noise of the blade can be eliminated, and images with high resolution can be kept for a long time. That is, in the conventional configuration, merely applying the lubricant produces a thick liquid film without evenness at all and, therefore, toner tends to be attached and images tend to be disturbed. However, in this image forming apparatus, with an applying brush as a brush-shaped rotating body, operations of applying the lubricant onto the brush, evenly spreading the applied lubricant over the surface of the photosensitive material, and polishing can be achieved.
Still further, an image forming apparatus has been known, which includes a cleaning unit that cleans the surface of a moving member, such as a photosensitive material or a transfer belt, with toner attached thereto, wherein the cleaning unit includes a cleaning blade formed of a rubber compact and a cleaning brush rotatably making contact with the surface of the moving member, and a conductive roller that cleans the surface of the moving member, the conductive roller with a predetermined bias being applied thereto, and a low friction portion is provided near an edge of the cleaning blade (for example, refer to Japanese Patent Application Laid-Open No. 2002-287592 (pp. 2-4, FIG. 1)). Also, in this image forming apparatus, the cleaning brush is configured to be conductive and is applied with a bias to electrically remove toner. Furthermore, the brush is rotated to mechanically remove toner. Still further, at least one portion of the cleaning brush is configured to have a portion where brush bristles are formed in a loop. Therefore, according to this image forming apparatus, since a low friction portion is provided near the edge of the cleaning blade, toner that cannot be removed by the cleaning brush can be removed by the cleaning blade. Also, even if the amount of toner onto the cleaning blade is small, the blade does not curl up, thereby keeping an excellent cleaning state. Still further, in a configuration allowing toner removal by the cleaning brush to be performed in an electrical and mechanical manner, more reliable toner removal can be made. In a configuration having loop-shaped brush bristles partially included therein, foreign substances that cannot be removed by the cleaning blade can be removed, thereby ensuring excellent cleaning ability.
Still further, an image-carrier cleaning apparatus has been known which at least includes: a cleaning brush formed in a roll shape that rotates and makes contact with a carrier surface after toner image transfer to slidably scrub the carrier surface; a cleaning blade that is pressed against the carrier surface at a downstream side of the cleaning brush in the movement direction of the carrier surface and scrapes residual toner from the carrier surface; and a flicker member for removing the toner attached to the cleaning brush from the cleaning brush, wherein the flicker member is provided with a solid lubricant, and the solid lubricant is applied onto the carrier surface of the image carrier via the cleaning brush to control a coefficient of friction of the carrier surface of the image carrier (for example, refer to Japanese Patent Application Laid-Open No. 2001-235987 (pp. 4-7, FIG. 1)). Therefore, according to this image-carrier cleaning device, a dedicated holding unit for holding a lubricant is not required. Thus, the conventional cleaning device can be inexpensively achieved almost without being increased in size.
Another image forming apparatus has been known in which a cleaning unit having a brush roller removes toner remaining on an image carrier after transfer, wherein brush bristles forming the brush roller are filled in a direction to form a tilt angle with respect to the direction of the normal to the rotational axis of the brush roller, the brush roller is pressed against the image carrier so that the tilt direction of filling the brush bristles at a position in contact with the brush roller is opposite to a rotating direction of the image carrier at the contact position, and a portion near the tip of the brush bristles is rotated as being pressed against the surface of the image carrier to slidably scrub that surface (for example, refer to Japanese Patent Application Laid-Open No. H10-282854 (pp. 5-11, FIGS. 2 to 4)). Therefore, according to this image forming apparatus, the tips of the brush bristles make contact with the perimeter surface of the image carrier to form an acute angle, thereby removing the developing agent from the image carrier in a scraping manner. Thus, clogging of the developing agent among the brush bristles of the brush roller can be mitigated, thereby keeping stable cleaning ability for a long time and solving an overflow of the developing agent. Also, driven rotation of the brush roller by the rotation of the image carrier is conventionally difficult because of a small coefficient of friction of the surface of the brush roller. By contrast, the brush bristles are filled in a direction opposite to the rotating direction of the image carrier. Therefore, the coefficient of friction of the roller surface is large, thereby allowing driven rotation. Thus, a simple structure without requiring a dedicated driving mechanism can be achieved. Such a structure is effective in saving space and reducing manufacturing cost.
Another cleaning device has been known in which residual toner on a photosensitive material after transfer is removed by a cleaning brush and a cleaning blade, wherein the cleaning brush is configured by winding a band-shaped brush member around a shaft, the brush member is configured by filling four and three fiber bundles each being formed of a bundle of insulating fibers and a bundle of conductive fibers as a unit for every 11 millimeters in a fabric-width direction of a base fabric, the fiber bundles being in W-weave in row, with a space in a width direction of each fiber bundle being set to 2 millimeters to 3 millimeters, a width of W-weave being set to 2 millimeters to 4 millimeters, and a space between three bundles and four bundles being set to 0.5 millimeters to 1.5 millimeters, the width of the base fabric being 30 millimeters, and a pitch of winding around the shaft being set as 1.1 times to 1.4 times wider than the width of the base fabric (for example, refer to Japanese Patent Application Laid-Open No. H6-236134 (pp. 3-5, FIGS. 6 and 7)). Therefore, according to this cleaning device, toner and additives are prevented from being accumulated among the brush fibers of the cleaning brush to harden the brush as a whole. Also, there is no need to reattach the removed additive to the photosensitive material. Thus, the additive on the photosensitive material can be excellently removed without any damage on the photosensitive material.
However, in the conventional configurations described above, a member equivalent to a flicker for cleaning by flicking attachments from the brush bristles of the cleaning brush roller is provided. Due to a flicking operation of this flicker simultaneously occurring over an entire area in a longitudinal direction of the brush roller, there is a problem of decreasing image quality.
That is, in the case where the bristles of the cleaning brush rollers are aligned in a direction parallel to the roller axis, when toner is scraped by the flicker, the brush bristles simultaneously make contact with the flicker over the entire area in the longitudinal direction of the brush roller, and also simultaneously go away from the flicker over the entire area in the longitudinal direction. As such, since making contact and going away are repeated, there is a problem in which the flicker is vigorously vibrated. That is, all brush bristles aligned on a line in the longitudinal direction of the brush roller simultaneously make contact with and go away from the flicker, a timing of occurrence of a reaction force due to a contact of the brush bristles aligned in the roller's longitudinal direction with the flicker is almost the same as a timing of disappearance thereof. Therefore, a large force is intermittently exerted on the flicker at the time of rotation of the brush roller. As a result, the flicker is caused to be vigorously vibrated. In particular, rotation of the brush roller at high velocity causes vibration to be more fierce. In the case of a configuration using loop-shaped brush bristles for increasing toner-removing ability, it is known that energy of vibration is also increased compared with a straight-bristle brush.
Such flicker's vibration is propagated to the photosensitive material, causing rotation unevenness of the photosensitive material (variations in velocity of the photosensitive material). This causes variations in density in a sub-scanning direction called banding to appear on an image, thereby degrading image quality. Such a state is depicted in FIG. 11. The frequency of vibrations is represented by (CI/P)×ω Hertz, where the circumference of the cleaning roller is CI millimeters, a filling pitch in a circumferential direction is P millimeters, and the number of rotation is ω rev/s.
In the configuration disclosed in Japanese Patent Application Laid-Open No. H10-282854, the bristle-filling direction of the cleaning brush roller is regulated. However, what is defined is the tilt angle with respect to the direction of the normal to the rotational axis of the brush roller, and the bristle-alignment direction in a rotational-axis direction of the brush roller is not regulated. Therefore, in a manner similar to that described above, the brush bristles simultaneously make contact with and go away from the image carrier repeatedly over the entire area in the longitudinal direction of the brush roller. Rather, the tilt direction of filling with the brush bristles is set to be opposite to the rotating direction of the image carrier. That is, the brush bristles are tilted forward in a direction in which the brush bristles advance. Thus, when a scraper serving as a flicker makes contact with the brush bristles, the degree of bending the brush bristles is large. Accordingly, the reaction force caused by the brush bristles is increased to cause vibrations of the flicker to be more fierce.
Also, in the configuration disclosed in Japanese Patent Application Laid-Open No. H6-236134, no mention is made to a relationship between a flicker bar serving as a flicker and vibrations, Furthermore, the bristle-alignment direction on the outer perimeter of the brush roller depicted in partial front views of the brush roller in FIGS. 5 and 7 seems to be aligned with the roller's longitudinal direction. That is, various space dimensions, width dimensions, and pitches set as described above result in regularity in which the bristle-alignment direction is aligned with the roller's longitudinal direction. In particular, as clearly depicted in FIG. 7, grouped brush bristles are regarded as being arranged to be spaced a predetermined distance apart from one another in a circumferential direction on the perimeter of the brush roller and be roughly aligned with the roller's longitudinal direction, although in a slightly tilted direction. In the end, according to rotation of the brush roller, the brush bristles simultaneously and intermittently make contact with and go away from the flicker in units of groups.